Tumor specific T cells, derived from cancer patients, will bind and lyse tumor cells. This specificity is based on their ability to recognize short amino acid sequences (epitopes) presented on the surface of the tumor cells by MHC class I and class II molecules. These epitopes are derived from the proteolytic degradation of intracellular proteins called tumor antigens encoded by genes that are either uniquely or aberrantly expressed in tumor or cancer cells.
The availability of specific anti-tumor T cells has enabled the identification of tumor antigens and subsequently the generation of cancer vaccines designed to provoke an anti-tumor immune response. Anti-tumor T cells are localized within cancer patients, including in the blood (where they can be found in the peripheral blood mononuclear cell fraction), in ascites fluid in ovarian cancer patients (tumor associated lymphocytes or TALs) or within the tumor itself (tumor infiltrating lymphocytes or TILs). Of these, TILs have been the most useful in the identification of tumor antigens and tumor antigen-derived peptides recognized by T cells.
Conventional methods to generate TILs involve mincing tumor biopsy tissue and culturing the cell suspension in vitro in the presence of the T cell growth factor interleukin-2 (IL-2). Over a period of several days, the combination of the tumor cells and IL-2 can stimulate the proliferation of tumor specific T cells at the expense of tumor cells. In this way, the T cell population is expanded. The T cells derived from the first expansion are subsequently mixed with irradiated tumor cells and cultured in vitro with IL2 to promote further proliferation and enrichment of tumor reactive T cells. After several rounds of in vitro expansion, a potent anti-tumor T cell population can be recovered and used to identify tumor antigens via conventional but tedious expression cloning methodology. Kawakani, Y. et al. (1994) PNAS 91(9):3515-19.
This currently employed methodology used to generate tumor specific T cells in vitro is unreliable and the antigens identified by this method do not necessarily induce an anti-tumor immune response. Numerous experiments demonstrate that encounter of antigens by mature T cells often results in the induction of tolerance because of either ignorance, anergy or physical deletion. Pardoll (1998) Nature Med. 4(5):525-531.
Thus, a need exists to identify antigenic peptides that will induce an immune response for the generation of effective anti-cancer vaccines. This invention satisfies this need and provides related advantages as well.